This study examines the efficacy of erythromycin and clindamycin in eradicating renal cysts and establishes the levels of these antibiotics that penetrate cysts localized in different sites of the nephron. Inulin and PAH clearances are determined for each subject prior to surgery. Serum, urine, and cyst fluid are obtained at surgery and receive detailed bacteriologic study. These fluids are analyzed for electrolytes, osmolants, urea, creatinine, inulin, and PAH.